1. Field of the Invention
The present invention relates to an optical data recording/reproduction apparatus which optically records signal on a recording medium by applying a light source, such as a laser beam, and reproduces the recorded signal. More particularly, the invention relates to a tracking control apparatus which causes light spot focused on the recording medium to trace a signal track and to jump to a predetermined track.
2. Description of the Prior Art
There are conventional optical data recording/reproduction apparatus which focus and irradiate a light beam generated from a light source, such as a semiconductor laser, on a recording medium of a disc rotating for a predetermined number of rotations before eventually recording and reproducing data signals. The recording medium is provided with a large number of data recording/reproduction tracks each having a 1.2 micron width and 1.6 micron pitch in a spiral or concentrically circular form. In order to record a signal on the tracks or reproduce a signal recorded on the tracks, these optical recording/reproduction apparatus execute a focussing control operation to focus a light beam on the recording medium in order that an extremely fine light spot having a maximum diameter of 1 micron can be generated, while the optical recording/reproduction apparatus also executes a tracking control operation so that the extremely fine light spot can correctly trace the center of the signal-recording track.
Normally, these conventional tracking control apparatus are composed of the following: a photodetector which detects the tracking-deviated signal by applying the reflected light of a light beam subjected to the influence of diffraction in the signal recording/reproduction track or by applying light which has permeated the recording/reproduction medium; a circuit means which provides the detected tracking signal with phase-compensation, and an actuator which drives an objective lens or a galvano mirror in order to transfer the light spot in a direction which is almost 90.degree..sub.-- apart from the signal track. Each 5.25-inch optical disc has about 18,000 tracks. In order to record and reproduce signals on and from the desired track, the optical disc recording/reproduction apparatus transfers the light spot in a direction which is almost 90.degree..sub.-- apart from the signal recording/reproduction tracks before accessing the desired track. The transfer of the light spot between signal recording/reproduction tracks on the disc is called a "track-jumping" operation.
As was typically disclosed in the Japanese Laid-Open Patent Publication No. 62-200534 of 1984, any conventional optical data recording/reproduction apparatus discontinues the tracking control operation before driving the tracking actuator in the desired direction by applying a pulse signal. As soon as the tracking actuator arrives at the halfway position on the way to the desired track, the conventional system drives the tracking actuator in the opposite direction, and then as soon as the tracking actuator arrives at the desired track, the system resumes the tracking control operation by performing the track-jumping. In other words, since the conventional system discontinues the tracking control operation to perform the tracking jumping by applying pulse signal for driving the tracking actuator, the conventional system cannot fully stand external disturbances, such as vibration, incurred by the servo system while the track-jumping operation is underway, thus unavoidably resulting in an unstable track-jumping operation.